The invention relates to a liquid crystal eyeglass, and more particularly, to a liquid crystal eyeglass which is capable of automatically preventing a deviation in the focal length from a preset value from occurring in response to a temperature change and also to a power supply which feeds a voltage applied to the liquid crystal.
When the function of adjusting the focal length in the eyeballs is degraded as with presbyopia, eyeglasses of different focal lengths which may be used for near and far distances are commonly used, and must be changed depending on the situation. There are some single eyeglass lenses which are partly provided with a region having a different focal length so that suitable ranges at near and far distances can be covered. However, it is only in a portion of the field of sight which is in focus, causing a painful view.
When the crystalline humor is extracted because of a disease such as cataract, several eyeglasses having different focal lengths must be provided and must be chosen in use depending on the situation, thus causing an inconvenience.
To accommodate for this, there is disclosed in Japanese Patent Publication No. 50,339/1983 to provide a variable focal length lens comprising a voltage controlled liquid crystal. This construction operates with a low voltage and with a low power dissipation, and can be conveniently used as far as this aspect is concerned. However, when it is used as eyeglasses, the refractive index of the liquid crystal varies with a temperature change and hence prevents a clear sight. It is understood that the environmental temperature greatly varies from season to season and also undergoes a large variation between the outdoor and the indoor condition which is air conditioned during the summer or winter. Thus, the described arrangement disadvantageously requires an adjustment in the applied voltage in response to any change in the surrounding temperature. As another drawback, a bulky power supply box for the liquid crystal must be contained as in a pocket of a suit which is typically located in the region of the breast.